I'd call some of the Better Bottle dealers and ask for a special price based on your quantity. Shipping is not bad as they are very light. You can't go wrong with Better Bottles. You back will thank you and you feet will too if you ever drop one on a toe.

PS - This store is great for homebrewing supplies of all types, not just carboys. They have bottles sometimes, glassware for serving, various utensils, mason jars for yeast washing, etc. Also I bought a 5 gallon stainless steel pot there for like $15 and it's very good quality.